Stopwatch seconds kinda breaks when it reaches 10. Any help?

I've been trying to make a stopwatch for an obby game of mine, which times you as you complete it. When the stopwatch reaches 10 however, it breaks and say "00:010" instead of "00:10" like its suppose to. If anyone could help, that would be great.

Its inside a local script with its parent being a textlabel.

local startmin = 0
local startsec = 0
local text = script.Parent
local min = 0
local sec = 0

while true do
    startsec = startsec + 1
    print("Added 1 sec")
    if startsec == 60 then
        startsec = 0
        startmin = 1
    end
    if sec > 9 then
        local mess = "0" .. startmin .. ":" .. startsec
        text.Text = mess
    else
        local mess = "0" .. startmin .. ":0" .. startsec
        text.Text = mess
    end
    wait(1)
end